WASHINGTON (AP) — Freeing 276 Nigerian girls from the terrorist group Boko Haram is now one of the U.S. government’s top priorities, U.S. officials declared Thursday, issuing warnings about the militant group’s expanding reach and growing capacity for more sophisticated and deadlier terror attacks.

At the same time, the officials lamented limitations on U.S. cooperation and intelligence sharing with the Nigerian military due to human rights concerns and legal restrictions. They also expressed concern about the Nigerian government’s commitment and army’s ability to combat the group.

Robert Jackson, a State Department specialist on Africa, said that Boko Haram “has no regard for human life.” He said the Obama administration was boosting Nigeria’s intelligence and law enforcement capabilities, while seeking global sanctions on Boko Haram at the United Nations.

The girls’ abduction last month from a school in the remote Nigerian town of Chibok triggered global outrage. The extremist Islamist militants have threatened to sell the girls into slavery.

“Resolving this crisis is now one of the highest priorities of the U.S. government,” Jackson told a Senate Foreign Relations subcommittee. Boko Haram, he said, “has been killing innocent people in Nigeria for some time, and the attack at Chibok is part of that long, terrible trend.” The group has killed more than 1,000 people this year in attacks on schools, churches and mosques and now poses a growing threat to neighboring Cameroon, he added.

Testifying alongside Jackson, Alice Friend, the Defense Department’s principal director for Africa, said Boko Haram was becoming more dangerous by the day.

The group has proven it is “capable of directly and successfully engaging Nigeria’s armed forces,” she said.

“In general, Nigeria has failed to mount an effective campaign against Boko Haram,” Friend told the panel. “In the face of a new and more sophisticated threat than it has faced before, its security forces have been slow to adapt with new strategies, new doctrines and new tactics.” She said Nigeria’s own record of atrocities committed by security forces fighting Boko Haram is “even more troubling.”

Friend said the U.S. has programs to help Nigeria’s counterterrorism efforts. These include operations to snuff out bomb plots and provide better coordination between civilian leaders and the military. The U.S. also is trying to foster greater cooperation with neighbors Chad, Niger and Cameroon.

Pressed by Sen. Jeff Flake, a Republican, Friend acknowledged that U.S. assistance was being hampered by American restrictions on providing any military aid or training to security units even suspected of gross human rights violations.

The so-called Leahy law “affects assistance very much,” Friend said, because it is hard for the U.S. to find Nigerian units clean enough to qualify for support. However, she said Washington has identified divisions that can be backed and noted that intelligence sharing with Nigeria’s military isn’t bound by the law.

Jackson said an 18-member U.S. team began working in Nigeria earlier this week to provide law enforcement and intelligence assistance. The effort includes manned plane flights and drones. He said the administration was urging Nigeria to better protect human rights as it fights terrorism.

Included in the U.S. support team are two military experts who had been involved in the fight against the Lord’s Resistance Army, a militant group originally from Uganda but similarly operating across borders. Boko Haram’s terror strategy in many ways copies that of the LRA, Jackson noted.

Like Boko Haram now, the LRA leader Joseph Kony previously has prompted worldwide opposition and an international campaign on social media to defeat his group.